1. Field of the Invention
The present invention relates to machine tools in general.
More particularly, the invention relates to an arrangement for machining portions of a workpiece, such as e.g. a crankshaft, which are offset from the main axis of the workpiece and are also angularly offset with reference to one another.
2. The Prior Art
Machine tools are known for machining e.g. grinding or turning portions such as pins or trunnions of a larger workpiece, if these portions are arranged centrically with reference to the main workpiece axis. This is a relatively simple undertaking.
The operations become more difficult if the portions to be machined are offset from the main workpiece axis and are, in addition, angularly offset with reference to one another, as is the case with e.g. the crankpins of a crankshaft. The machine tool then requires equipment which is capable of positioning at least the particular portion to be machined so that it can move in a circular rotary path, rather than in an orbital path which it would normally assume when the overall workpiece is rotated. In addition, the workpiece must be readjusted and clamped each and every time a different one of these offset portions is to be machined; what is more, the portion must be located at an exactly prescribed angle relative to the machine. All of this is much too complicated to permit series operation, i.e. to permit large scale machining of identical workpieces.
It has been proposed to overcome these difficulties by providing machine tools with devices which can move the offset workpiece portions to a centric position for machining purposes. Another proposal is for equipment capable of making the portions assume the required angular position without having to release, reposition and reclamp the entire workpiece. Although these proposals constitute without doubt an improvement over the preceding state of the art, they are nevertheless far from satisfactory. This is especially true if the machine tool is to be used for the series-manufactured of a specific workpiece, i.e. for an operation in which the same operations must be repeated again and again with great accuracy. To make such operations economically feasible they must be capable of being largely automated which was not possible with the prior equipment.